Emphasis will be placed on the purification of extracellular polysaccharidases from fungal and bacterial pathogens that degrade the polymeric carbohydrates of the plant cell wall. The enzymes of particular interest include the pectic enzymes (endopolygalacturonase, expolygalacturonase, endopolymethylgalacturonase, endopolygalacturonate lyase, and exopolygalacturonate lyase), arabanase, galactanase, xylanase, mannanase, and cellulase. Purification of these enzymes from culture filtrates and from diseased tissues will involve ammonium sulfate fractionation, ion exchange chromatography, electrofocusing, and such other procedures as may be necessary, i.e. substrate affinity chromatography. These enzymes are to be used individually and in various combinations in an attempt to determine their respective roles and relative importance in the alteration of plant cell walls during pathogenesis, and to elucidate plant cell wall structure.